Rakata
The Rakata are an amphibian-humanoid species from the planet Lehon. They ruled an "Infinite Empire" of 500 worlds, several thousand years before the formation of the Republic. They are believed to be responsible for Tatooine's desert climate due to their razing of the planet, and Kashyyyk's lush overgrowth from their terraforming. During the travels of Revan (Knights of the Old Republic), it is discovered that this race went into decline due to the combination of a civil war and genetic plague. It is not known exactly when this happened, but around 3000 years after their discovery they became extinct. The Rakata also used their amazing technological skills and knowledge to build a massive space station called the Star Forge.
Read more about this topic: List Of Star Wars Species (P–T)